Back to the half-season high-flyers, and we move into the realm of the "repeat offenders," starting with the hitters who managed two half-seasons in the Top 300 of either first-half or second-half standout performances.
We'll break up this sort into four segments, with some brief comments and a summary at the end. First, we go back to modern baseball's "dawn of time"...
We'll give away the subtext here at the outset: players in bold type are the ones who've been elected to the Hall of Fame. We'll add that total up for each grouping--the one-timers, two-timers, three-timers, and on up.
Here in the Deadball era, you have two-timers who mostly have shorter careers (and who weren't teammates of Frankie Frisch), so only one hitter (Frank Chance) has made it into the HOF. Of the other seven on this list, Jimmy Sheckard and Sherry Magee probably have the most compelling cases for induction, but Cy Seymour and Mike Donlin had the most impressive half-seasons.
In using a list of this type, we'd tend to weight its relevance for Hall of Fame eligibility based on how many different seasons are represented in the "top half-season" groupings. Thus two-timers like George Stone and Steve Evans, whose peaks are encompassed in the same season, are grouped a bit lower because they simply had a "career year."
Our eight two-timers in the 1920-1959 time frame have fared better relative to the Hall of Fame: five of them have been inducted (only one, Chick Hafey, is part of the Frisch contingent--but Hafey is part of the subgroup who managed to hit .400 in a half-season--and the 1931 NL is not the huge offensive year that you might be assuming, given its proximity to 1930). The top half-seasons (as measured by OPS+) belong to George Sisler in 1920 and Roy Cullenbine in 1946, with the latter exceeding a .500+ OBP in each of his half-season peaks.
Another group of eight, with three in the Hall. Given the time frame, batting average and OPS is depressed somewhat; the best half-seasons here (according to OPS+) are turned in by John Mayberry, who gave Dick Allen a run for his money in the second half of 1972 after a lukewarm start (and was equally impressive in the second half of 1975). Fred Lynn made plenty of waves in the first half of 1975 with one of the most celebrated rookie performance levels of all time (but that was back when the Red Sox still had their tragic mystique). And if you don't think there can be a major difference in offensive levels from one season to the next, take a look at Wade Boggs' half seasons in 1987 and 1988. The latter season is actually more impressive relative to the "adjusted strike zone" imposed after the '87 homer glut, and that's captured in the fact that Boggs hit fourteen fewer HRs in '88 and still had a superior OPS+.
In the past thirty years, we've had twelve more two-timers, with only the first two (Jeff Bagwell and Jim Thome) having thus far made it to Cooperstown. As has been the case of late, only sluggers need apply: twenty of the twenty-four half-seasons shown above are ones where batters hit 20+ homers. Two hitters here--Jose Bautista and Christian Yelich--have "adjacent peaks" that span the second half of one season and the first half of the next: putting those two segments together reveals that Bautista hit 61 HRs in 157 games in his crossover seasons, while Yelich hit 56 in his 144-game "wraparound year."
All in all, eleven of our thirty-six "two-timers" have made it into the Hall of Fame. That's just under a third (31%). We'll track this rate as we move "up the food chain"--up next, the three-timers...
